In recent years, many types of filter have been used in small communication devices, such as cellular telephones. Great demands for reductions in the size, profile, and weight of small communication devices also require reductions in the size, profile, and weight of such filters. Furthermore, in the small communication devices, an increase in the amount of information required to be communicated, for example, the increase of communication of images, has led to the communication frequencies being increased to GHz frequencies or higher.
Therefore, with such trends toward higher communication frequencies, piezoelectric filters and surface acoustic wave filters have been used as the above-described filters.
Each of the piezoelectric filters includes a plurality of piezoelectric resonators connected so as to form a ladder network or a lattice network. The piezoelectric resonators each include, for example, a Si substrate having an opening or a depression and an exciter provided on the Si substrate, the exciter covering the opening or the depression, and the exciter having a structure in which the upper and lower surfaces of a thin film portion having at least one piezoelectric thin film (composed of ZnO or AlN) are sandwiched between at least one pair of an upper electrode and a lower electrode, the upper electrode being disposed opposite the lower electrode. In such a piezoelectric filter, longitudinal oscillations generated along the thickness direction of the exciter are used; hence, it is necessary to ensure a space for the oscillations above the exciter and to protect the exciter from exposure to water, dust, and the like.
Each of the surface acoustic wave filters includes an interdigital electrode provided on a piezoelectric substrate composed of, for example, quartz, LiTaO3, or LiNbO3. In such a surface acoustic wave filter, it is necessary to ensure a space for oscillations above a propagation portion for surface acoustic waves on the interdigital electrode and the piezoelectric substrate and to protect the interdigital electrode from exposure to water, dust and the like.
As disclosed in Japanese Unexamined Patent Application Publication No. 5-275965 and shown in FIG. 14, in a known piezoelectric electronic component including a piezoelectric filter or a surface acoustic wave filter, a die bonding agent 75 is applied to the bottom surface of a box-shaped package 73 composed of alumina or the like, and a piezoelectric element 71, such as a piezoelectric filter or a surface acoustic wave filter, is mounted in the package 73 by die bonding. After bonding terminals in the package 73 to the corresponding electrodes of the piezoelectric element 71 with bonding wire 77, the opening of the package 73 is sealed with a lid 79 using solder 79a. 
As disclosed in Japanese Unexamined Patent Application Publication Nos. 2002-232253 and 2000-49565, to enable a reduction in size, electrode lands are formed on the inner bottom surface of a package composed of alumina or the like, a piezoelectric element, such as a piezoelectric filter or a surface acoustic wave filter, is mounted on the electrode lands by flip-chip bonding. Then, the package is sealed with a lid.
However, in such a known structure, if a piezoelectric element, such as a piezoelectric filter or a surface acoustic wave filter, is reduced in size and profile, unless the package is also reduced in size and profile, the total size of a piezoelectric electronic component including the piezoelectric filter or a surface acoustic wave filter cannot be reduced, which is disadvantageous. Furthermore, in such a known structure, the package is often composed of a poorly processable material, such as alumina; hence, a reduction in the size of the package disadvantageously increase the process cost of the package.
In particular, in the piezoelectric filter, the exciter is provided at the opening or the depression of the substrate. Thus, impacts on the exciter in processing steps, such as dicing a piezoelectric element, picking up the piezoelectric element in mounting, and die bonding, can cause the destruction of the exciter, thereby disadvantageously reducing the yield of the resulting piezoelectric electronic components, prolonging time required for dicing, and increasing cost.